Generally, as water-resistant and moisture-proof paper, paper coated with a polyolefin type resin such as polyethylene, polypropylene or the like is well known and widely used. This water-resistant and moisture-proof paper extrusion-laminated with such a polyolefin type resin not only has excellent water-resistance, moisture-proofness and processability, but also is economical and remarkably excellent as water-resistant and moisture-proof paper. For this reason, this paper is in wide use as a wrapping paper for paper products requiring moisture-proofness, packages for plastic pellets, salt and the like. Moreover, in this industry, there is also moisture-proof paper called clad paper or poly-sandwiched type, in which two sheets of paper are bonded with the polyolefin resin sandwiched therebetween. Further, the polyolefin resin is excellent in water-resistance and heat-sealability and is thus easily processable, it is widely used as paper cups for drinks and cow's milk packages, too.
On the other hand, from a view point of recycling property, that is, wastepaper regenerability, the mechanical strength of the laminated film of the moisture-proof layer of the water-resistant and moisture-proof paper coated with a polyolefin is too high and therefore, a pulper to be employed in a process of regenerating paper and carrying out pulping cannot finely disperse the polyolefin type resin layer parted from the fibrous part of the paper and leaves the resin layer as blocks and films, and they are stuck to a drying roll of a paper making machine or adheres to the surface of regenerated paper or causes bleeding and surface roughness to thus make recycling of wastepaper impossible. Accordingly, in this industry such paper coated with a polyolefin resin is positioned as taboo products of non-recyclable materials, together with photos, laminate labels or the like. In addition, in recycling milk packages, every endeavor is made to beforehand remove a polyethylene film coated.
Further, in light of moisture-proof paper possible to be recycled being demanded, moisture-proof paper coated with an emulsion containing a synthetic rubber latex or an acrylic emulsion and a wax emulsion has recently been proposed. Although this moisture-proof paper is certainly excellent in moisture-proofness and also in recycling property as wastepaper, since the coating liquid is an aqueous emulsion, large scale drying facilities are required to form the coating layer, which leads to increase both in equipment cost and in energy cost and the productivity is inferior as compared with the case of laminating with a polyolefin type resin. In addition, with proceeding of the drying and the coating film of a moisture-proof layer, the moisture-proof paper is sometimes curled and the wax in the coating layer sometimes bleeds, and slippage sometimes occurs between moisture-proof papers. Moreover, in the case where the obtained moisture-proof paper is rolled like a coil, since the face of the moisture-proof layer is brought into contact with the opposed face in which no moisture-proof layer is formed, the wax components contained in the moisture-proof layer are transferred to the opposed face, which results in problems that slippage is considerably easily caused. Moreover, it is pointed out that the wax layer is formed on the surface of the moisture-proof layer so that printing with an aqueous ink is impossible and an emulsion adhesive for packaging paper can not be used. Further, in recycling of wastepaper, water-soluble ingredients forming the emulsion dissolve into a waste liquid for manufacturing paper and thus the treatment of the waste liquid becomes difficult.
Moisture-proof paper is also proposed which blends a large amount of a flat-shaped inorganic filler into the aforementioned latex or emulsion to make use of moisture-proofness of the inorganic filler. By blending the flat-shaped inorganic filler, most of drawbacks caused by the wax are solved, but a fresh problem is brought about by the inorganic filler blended in a large amount is pointed out. That is, those are fatal drawbacks as a wrapping paper that the moisture-proofness at a folded part of the moisture-proof paper is liable to lower and that the surface of paper products wrapped tends to be damaged by the inorganic filler. In addition, the difficulty in waste water treatment is not solved.
Moreover, in the case of the moisture-proof paper using a latex or emulsion type moisture-proof liquid, there are many problems when it is used for foods in direct contact with the moisture-proof layer. That is, since an emulsifier, a film-forming agent or the like contained in the latex or emulsion remains in the moisture-proof layer, there is a fear of transferring them to the foods. In addition, there is a problem with respect to water resistance caused by the influence of those residual impurities.
The purpose of the present invention is to solve the conventional drawbacks as mentioned above and to provide a resin composition for obtaining a water-resistant and moisture-proof paper which can be disaggregated and a water-resistant and moisture-proof paper using the composition.
In light of the numerous problems included in a polyolefin-laminated moisture-proof paper which is widely used but cannot be disaggregated, the present inventors have made an extensive series of studies on a resin composition which can be disaggregated and have found out that by blending a large amount of a tackifier with a polyolefin resin, it is possible to obtain a water-resistant and moisture-proof paper which can be disaggregated by a pulper or the like, while making use of the excellent moisture-proofness of the polyolefin resin.
The resin composition in a first aspect of the present invention does not require a large amount of a wax or an inorganic filler as an indispensable component so that it is free from slippage and a decrease in heat resistance caused by the wax. Moreover, it does not require an inorganic filler of a specific shape, either, and thus it has numerous advantages that it is free from a decrease in moisture permeability at the folded portion and a damage of the surface of paper products wrapped, or the like.
Further, since the resin composition does not contain water-soluble harmful substances such as an emulsifier and a film-forming agent, there is little substance dissolving into water for making paper when pulped for the regeneration of wastepaper, which does not increase a load to the treatment of waste water.
The resin composition in a second aspect of the present invention not only solves the problem of high expense of the foregoing resin composition as compared with the conventional polyethylene-laminated moisture-proof paper by blending an inorganic filler, but also solves the drawbacks associated with the conventional moisture-proof paper making use of the moisture-proofness of an inorganic filler, i.e., fatal problems as a wrapping paper such as a decrease in moisture-proofness at the folded part and damage of the surface of paper products wrapped.